The outer membrane of Escherichia coli contains proteins which serve as specific receptors for certain nutrients, colicins and phages. Goals of this project include the genetic and biochemical characterization of these receptors and the other components involved in the uptake of their ligands, the regulation of synthesis or activity of these components, the interactions of these components, and the mechanisms of ligand uptake. These transport activities require participation of the tonB product, which appears to provide energization to the receptor proteins; understanding of the action of this protein is crucial to this entire question of outer membrane-dependent transport processes. Aspects of the genetic analysis include mutants partially defective in receptor function or in certain tonB functions. Identification of genes possibly coding for cytoplasmic membrane components necessary for these uptake systems has been carried out with the transport systems for vitamin B12 and for chelated to hydroxamate-type chelators. Attempts to define the site of these gene products are under way with the use of cloned fragments carrying these genes. Attempts are continuing to develop an in vitro assay for the tonB function and to determine its location with the aid of specialized transducing phages. The interactions between components involved in outer membrane-dependent uptake are studied both by characterization of mutants and by formation of intergeneric hybrids. Within a year, these studies should give some understanding of the action of the tonB product on the outer membrane receptors.